Status and prospects of CDEX

Qian Yue

Tsinghua University

On behalf of CDEX Collaboration

Sept. 7, 2015

TAUP 2015 @ Torino

Outline：

• CDEX experiment introduction

• CDEX-1 results and CDEX-10 status

• CDEX-200 experiment plan

• Summary

TAUP 2015 @ Torino

China Darkmatter Experiment (CDEX)

• Nature of dark matter unknown.

• WIMPs is one kind of well

motivated candidate.

Recoil energy (keVee)

Target : Ge

Mass = 10 GeV·c-2

σSI

= 10-40

cm2

Point-contact HPGe detector (PCGe) :

Low energy threshold (~ 100eVee)

Very good energy resolution

Easy to scale up

CDEX target:

Direct detection of low

mass dark matter with

tonne-scale PCGe array!

Dark matter ～85%

~15%

TAUP 2015 @ Torino

Established in 2009.

• Tsinghua University, THU

• Sichuan University, SCU

• Nankai University, NKU

• China Institute of Atomic Energy, CIAE

• Yalong River Hydropower Company, EHDC

• Collaborate with TEXONO and KIMS group.

CDEX: China Dark matter EXperiment

part members of the CDEX collaboration

TAUP 2015 @ Torino

CDEX plan

1kgPCGe

1kg

PCGe

upgrade

DM sensitivity（cm2）10-40 10-41 10-42 10-43 10-44 10-45

LN/LAr

10kg

PCGe

Array

CDEX

200CDEX-1T

CJPL-I CJPL-II

PCGe

Home-

Made

CDEX published physical papers：

PRD88, 052004, 2013

PRD90, 032003, 2014

PRD90, 091701, 2014

Electro-

form

Copper

LT/LN

LB VFE

CDEX-1 experiment1. HPGe technology

Designed the first one single module 1kg-scale p-type point-

contact Ge detector (1kg-PPCGe) C1A from 2011

Improved the second 1kg-PPCGe C1B from 2014

2. Active shielding technology: NaI(Tl) used as anti-Compton detector

C1A 1kg-PPCGe run

C1 20g Ge + NaI(Tl) run C0 from 2011

C1A 1kg-PPCGe + NaI(Tl) run

1kg-PPCGe NaI(Tl)TAUP 2015 @ Torino

CDEX-1

20g ULEGe

1kg PCGe

20cm OFHC Copper

+20cm Lead

6TAUP 2015 @ Torino

• The lowest energy threshold for

~1kg-scale PCGe detector: 400eV

• The first dark matter physical result

from China!

W. Zhao et al., Phys. Rev. D 88, 052004 (2013);

C1A 1kg-PPCGe

CDEX-1 experiment

TAUP 2015 @ Torino

CDEX-1 result from 20g Array detector

CDEX-1 5g*4 +AC detector

Highlight：

177eV lowest ionization

energy threshold

Good direction to lower

energy threshold further

PRD90,032003,2014

)2 ( GeV/ccM2 3 4 5 6 7 8 9 10 20

)2

( cm

SI N

cs

-4210

-4110

-4010

-3910

-3810

TEXONO 2013

XE

NO

N100

CDM

Slite

DAMA

CRESST-II

CoGeNT 2013

CDMS-II Si

CDEX-0

TEXONO 2007

CRESST-IL

UX

(This Work)

CDEX-1 2013

Projected )

-1day

-1keV

-1(10 kg-yr ; 100 eV ; 1 kg

SuperC

DM

S

SuperCDMS

CDEX-1 2014

• C1A + NaI(Tl) AC

• Bulk/Surf Discrimination

Q.Yue et al., PRD 90(RC) 091701

The best sensitivity by PCGe in the world;

Exclude the regions favored by CoGeNT.

CDEX-1 result in 2014

TAUP 2015 @ Torino

The development of DM experiment

Have no definite DM evidences in the low mass

and high mass regions;

Have spaces need to be scanned;

CDEX will focus on the low mass DM search.

Ge Xe Ar

CDEX-10 experiment

L

L

L

L LAr

GAr

HV and SignalsCooling and

Control

CDEX-10 experimental setup 10kg-PCGe + LAr

3-PCGe element

• The important stage towards large-scale Ge experiment!

• Performance study of the Ge array detector

• Feasibility study of LAr Anti-Compton detector

TAUP 2015 @ Torino

PPCGe array detector

Three 3kg PCGe detector

Pb + Cu 10mm

Cu 2mm

HPGe

TAUP 2015 @ Torino

The performance test of Ge array in CDEX-10

TAUP 2015 @ Torino

• Two 3kg PCGe Array detectors tested in CJPL;

• The energy thresholds and backgrounds are quite good for dark

matter experiment;

• The first results planed by the end of this year.

• Ge purification and Ge crystal growth

• HPGe detector fabrication

• Ultra-low background VFE

• Ultra-pure copper for structures and cables

• Large-volume cooling tank

• ……

Key technologies towards CDEX-200(1T)

TAUP 2015 @ Torino

Zone refining

machine

Czochralski

machineCutting &

Polishing

CDEX-1T –Ge crystal growth

Crystal growth

Achieved

Impurity density: ~5*1010 cm-3

The dislocation: ~5000 cm-2 in the center

The requirement for making P-type Ge detector

Impurity density: <3*1010 cm-3

Dislocation: <5000 cm-2

TAUP 2015 @ Torino

CDEX Lab for HPGe detector fabrication

• Clean room

• Wet Lab

Vacuum Coating

Machine

Magnetron

Sputtering

Device

• Machine-shop

Crystal Processing

Mechanical

Preparation

Lithium

Diffusion

Wet

Lab

Boron

Implant

• Typical Processing Technology is used

Boron Implant

Accelerator

HPGe detector fabrication

0 100 200 300 400

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Co

un

ts

Channel

241

Am

7#点电极

HV=350V， t=4us

Peak=323.99

1.48%@59.5KeV

Low Chan=10

Peak=50

~10KeV

500g point-contact Ge detector has been done successfuly,

comparable to the commercial product in energy resolution

Next plan: PCGe R&D with ultra-low energy threshold and

background used for dark matter experiment

0.177%

@1173keV

0.95%

@59keV

TAUP 2015 @ Torino

CJPL Electro-form Copper

Electro-form Copper produced in CJPL for CDEX ；

The Copper background now：Th:~44.66 Bq/kg、U:~149 Bq/kg

Our target in 5 years：Th<0.06 μBq/kg、U<0.17 μBq/kg (lower 1000 times)

Cooperation on Ge detector development

Ge meeting @ Munich on March, 2013

Ge meeting @ THU, Beijing on May, 2014TAUP 2015 @ Torino

CDEX-200

CDEX-200 with LN2

cooling system

CJPL-II development

• Total space:~300,000m³

• The LN2 cooling and passive shielding system：Goal: Background from outside of Ge < 10-4cpkkd

• The CDEX new space: 18m * 30m;

• CDEX-200 space ready in 2016.

CDEX-200 space in CJPL-II

• CDEX-1@CJPL has started to run detectors from 2011.

• DM physical results have been published in 2013 and

submitted in 2014.

• The 2014y CDEX-1 exclusive curve has disfavored

CoGeNT region with identical detector technique and

lower energy threshold. New results is coming.

• CDEX-10 with 10kg array detector tested in CJPL and

commissioning next month.

• CDEX-200 (2016-2020) preparing the space and key

technologies.

Summary

Thank you ！